The overall role of the Optics and Dosimetry Core, is to provide support for the light delivery for PDT both in the clinic and in the laboratory. This includes the setup of the light delivery devices (lasers, fibers, beam splitters) for both clinical and laboratory photodynamic therapy. PDT in both the laboratory and the clinic requires proper dosimetry. To perform this function it is necessary to understand the dosinletry of PDT, The limited understanding of dosimetry as dependant on the interaction of light and a drug has been expanded through study' of the QSAR data on the pyropheophorbide hexyl ether series to include a sensitive target for PDT. As more specific targeting is designed into PDT drugs we intend to continue to study the dosimetry of PDT in an attempt to support and provide a testable fralnework in which to understand the results of the projects in overall study of structure activity relationships. Core personnel will perform laser maintenance, calibration and dosimetric measurements required by the clinical and laboratory research activities of the prqiects. The specific support role functions of the Core are: 1. Teclmical support for the clinical and sciemific lasers of the clinical and laboratory programs of the Program Project. 2. Measuremem ofphotobleaching during therapy. 3. Measurement of the total attenuation of tumor and normal tissue in patients undergoing PDT for the treatment of skin tumors, and the hemoglobin absorption spectra. 4. Study of the pharlnacokinetics of the compounds symhesized by Proiect I. 5 Refining the analytic framework of PDT targeting and dosimetry.